Olefin polymer fibrils constitute a known class of fiber-like materials that are prepared by precipitating an olefin polymer from a solution thereof under conditions of high shear. See for example U.S. Pat. No. 4,013,751. Frequently the olefin polymer fibrils are refined with a polar organic liquid such as isopropanol and then treated with an aqueous solution of polyvinyl alcohol, with both treatment steps being carried out at ambient temperature, e.g., 20.degree. C., or a somewhat elevated temperature. This process, which is disclosed in U.S. Pat. Nos. 4,049,492 and 4,049,493, improves the fibrils' properties by a mechanism which has not been ascertained.